The invention pertains to alarm systems for warning the owner of a residence or other building containing a fireplace with a chimney, as to the hazard of a possible chimney fire caused by ignition of creosote progressively deposited over time on the chimney walls as a wood fire combustion product. Such creosote fires are often difficult to extinguish, and burn at a high temperature, which may exceed the chimney design limits, and thereby cause a general conflagration in wood frame members of the surrounding structure.
Although it is known to use a temperature sensor in a chimney to monitor a chimney fire hazard, the present invention offers means to directly detect light from a creosote fire, distinguished from the wood fire light, and to produce a corresponding alarm signal. In one form the invention also offers means to detect when the creosote temperature has reached a warning temperature nearing the creosote ignition temperature, and to produce a different warning signal when said warning temperature has been reached, as a preliminary warning signal.